This invention relates to devices and systems for controlling backup roll eccentricity and/or strip steering in rolling mill equipment for metals while using tapered roller bearings for the roll mountings. When rolling metal, the deformation force, i.e., the force required to reduce the thickness of the metal, is transmitted to the material through the mill housing, bearing chocks, bearings, roll necks and rolls, to the roll surfaces and into the metal strip. This means that all parts of the mill are stressed by the rolling load and all parts of the mill have a tendency to deform elastically. When the rolling load is applied, all the slack in the bearings, bearing chocks, screwdowns, and hydraulic cylinders is taken up. As the loading continues, the roller bearings have a tendency to deform and the rolls to flatten at the point of contact. Furthermore, the heat in the roll bites generates thermal crowns in the work and the backup rolls, and in addition to controlled coolant application to alleviate this deleterious crowning, a positive or convex mechanical camber is normally ground into the work roll to compensate for the same. During manufacture and subsequent grinding of the backup roll, however, backup roll eccentricity can occur. This eccentricity is the deviation of the axis of rotation at the barrel or main body portion of the roll relative to the axis of rotation of the same roll at its neck supports and is inherent in the manner and amount of precision with which the backup rolls are ground as well as the precision of the bearing components and their mountings.
Unless the aforesaid eccentricity is corrected, it will cause the work rolls to cyclically print out a gauge deviation pattern on the metal material being rolled. Various schemes and procedures have been suggested in the past for correcting this eccentricity problem, such as the complex-electronic measurement systems for detecting mill housing stretch or compression, due to changes in force at which the mill rolls engage the material being rolled, and using such measurements to control a roll actuating mechanism, such as hydraulic cylinders in the mill stands, to control the working space or gap of the mill work rolls. Examples of such systems are illustrated in the King et al U.S. Pat. No. 4,222,254 and Puda U.S. Pat. No. 4,531,392. These systems, however, are not truly precise in correcting the problem they attempt to solve, since they rely upon mathematical estimates of the eccentricity to be corrected because the actual eccentricity of the rolls does not appear to be readily observable. An attempt to overcome the deficiencies of the King et al control system and that of Puda is set forth in the Stewart et al U.S. Pat. No. 4,656,854, which is directed to use of an electronic system that continuously measures the tension of the rolled material entering or exiting a mill to indicate directly cyclic thickness changes in the material due to roll eccentricity and then using these measurements to control the roll actuators, such as hydraulic cylinders and, in turn, the working gap of the work rolls. None of the above eccentricity correcting systems, however, provides for a simple and completely satisfactory operation of the roll actuators per se, regardless of the efficiency of the remaining parts of the system. Proper operation of the actuators per se is critical to the successful operation of the eccentricity correcting system.
In addition to the above systems, various devices have been used in the past to bend backup or work rolls in order to improve flatness of the product being rolled, such as the roll bending devices of U.S. Pat. Nos. 3,442,109, 4,162,627, and 3,902,345. Other devices have used the concepts of laterally or axially shifting the work and backup rolls relative to each other, as illustrated in U.S. Pat. No. 3,943,742, or applying an axial thrust to the ends of the rolls to correct lateral shifting and/or thrust overloading of the rolls due to the stresses, such as thermal stresses, built up in the rolls during rolling, such as is illustrated in U.S. Pat. Nos. 3,973,425, 4,191,042, and 4,589,269.
None of the prror art devices or systems as represented by the aforesaid patents, however, has utilized the concept of applying separate and independent thrust forces to the various ends of the backup rolls and through the medium of tapered roller bearings for the said rolls in the unique fashion of the instant development in order to selectively and precisely change the rolling contour of the backup rolls and thereby compensate for backup roll eccentricity and the deleterious results that flow therefrom.